Structure Modification upon Ultrasonic Processing of an AA4032 Piston Alloy: Comparison of Permanent Mold and Direct-Chill Casting
Structure Modification upon Ultrasonic Processing of an AA4032 Piston Alloy: Comparison of Permanent Mold and Direct-Chill Casting
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DOI：
10.1007/s11661-019-05575-5
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发表时间：
2019-12
期刊：
影响因子：
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通讯作者：
S. Chankitmunkong;D. Eskin;Chaowalit Limmaneevichitr
中科院分区：
文献类型：
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作者：
S. Chankitmunkong;D. Eskin;Chaowalit Limmaneevichitr
活塞铝硅合金成分复杂，组织多相不均匀，必须控制初生相和共晶相的形成。在这项研究中，超声熔体处理（USP）的共晶铝硅活塞合金（AA4032型）进行在一个永久性模具和直接激冷（DC）铸造过程中，研究其对组织细化和修改的影响。这两种铸造方法之间的主要区别在于，在永久型中，凝固前沿逐渐向超声源移动，而在DC铸造中，凝固前沿的位置在空间上是固定的。结果表明，超声波能有效细化初生Si、Fe金属间化合物和铝晶粒。初生硅的细化伴随着其数量的增加，这归因于增强的异质形核和破碎。含铁金属间化合物和铝晶粒的细化导致的破碎机制，更明显的USP时，在永久模具中的液相线温度以下。然而，共晶相在USP上变粗，并且当USP应用于半固体材料时，这种效果最明显。这与声波的强烈衰减有关，声波有效地加热半固态材料并引起相的相应粗化。声流引起的振荡超声波发生器的影响的深度的水坑，同时减少宏观偏析，这反映了针对自然对流的熔体流动的主导作用。结果证明了USP应用的固化阶段的重要性以及USP机制在不同固化阶段起作用的具体情况。
Piston Al-Si alloys have very complex compositions and multi-phase heterogeneous structure, so it is necessary to control the formation of primary and eutectic compounds. In this study, the ultrasonic melt processing (USP) of a eutectic Al-Si piston alloy (AA4032-type) was performed in a permanent mold and during direct-chill (DC) casting to study its effects on the structure refinement and modification. The principal difference between these two ways of casting is that in the permanent mold the solidification front progressively moves towards the ultrasound source, while in the DC casting the position of the solidification front is fixed in space. The results showed that the USP can successfully refine primary Si, Fe-containing intermetallics and aluminum grains. Refinement of primary Si was accompanied by the increase in its amount, which was attributed to both enhanced heterogeneous nucleation and fragmentation. The refinement of Fe-containing intermetallics and Al grains resulted from the fragmentation mechanism and were more pronounced when USP was applied below the liquidus temperature in the permanent mold. However, the eutectic phases coarsened upon USP, and this effect was most pronounced when USP was applied to the semi-solid material. This was related to the strong attenuation of acoustic waves, which effectively heats the semi-solid material and induces corresponding coarsening of the phases. Acoustic streaming induced by an oscillating sonotrode affected the depth of the sump while simultaneously decreasing the macrosegregation, which reflects the dominant role of the melt flow directed against natural convection. The results demonstrated the importance of the solidification stage at which the USP was applied and the specifics of the USP mechanisms acting at the different stages of solidification.